Planet Escape Velocities affecting disassembly

Taking apart a planet for raw materials (perhaps for a Stady shell) is a frequent trope in innumerate, penny-a-word science fiction. However, unless solar system gravity constrains the mining process, more reaction mass will be lost diving in and out of the planet's gravity well than can be extracted from the planet - a "process gain" of less than unity.

A "recycling" extraction system will use some form of slow, high I_SP (electric?) engine to restore angular momentum between passes down into the target object's atmosphere to scoop some out (a very long term process ...). The recycler must remain bound in solar orbit in order to (eventually) return for another pass; if the target object's gravity well is deep, too much momentum will be expended as reaction mass outside the object's gravity well to make up for what is extracted deep in that well.

A crude estimate of the viability of extraction is the ratio planetary escape velocity to average planetary orbit velocity (in km/s below), which is the same as solar escape velocity for circular planetary orbits:

Minor bodies like the Kuiper belt (like Pluto), Oort cloud, and the asteroids are the best source of construction materials. They are also sources of Earth impact hazards, so after exhaustive study, they are the best objects to exploit first.

Of the major bodies, Mercury and the Moon have the best ratios - and no atmospheres. Those can use electromagnetic catapults to loft material directly into space for a capture vehicle to rendesvous with - viability "infinite". Pluto has a good ratio, and no significant atmosphere, another good candidate for eventual disassembly. Venus and Earth are marginal but remotely possible targets for disassembly; however, Earth is much more valuable as a living planet. Venus is the best candidate for terraforming; removal of carbon and crust, and the addition of a sunshade (made from some of that crust) could transform it into a sister Earth.

Mars is a poor target for permanent terraforming; too small. However, as a potential second cradle of life, it must be thoroughly explored for the ghostly residue of past microbes; the economic value of a biological "second example" vastly outweighs the economic value of Mars as a temporary, unhealthy, and high maintenance "fake Earth".

I won't argue with the "extreme environmentaloids" who would prohibit any interaction with the solar system; if they want to prevent harm to any astronomical object, they should protect the solar systems most interesting ecosystem and stop breathing.